This invention relates to novel composites useful for machine packaging electrostatic sensitive electronic components or assemblies to protect them from damages due to electrostatic discharge, electrostatic field force, radio-frequency interference, moisture, and corrosive gases.
Functional failures or manufacturability impairments of modern electronics components or assemblies are often traceable to damage due to electrostatic discharge, electrostatic field force, radio frequency interference, moisture, corrosive gases, and machine oil they may experience during shipping and storage. The problem has increased in severity in recent years and will continue to worsen because of the increased miniaturization and speed of devices and systems, like VLSI (Very Large Scale Integration) chips, the impact of new automated manufacturing processes such as high heat and chemical, e.g., oil, solvents, etc., exposure in a surface mount assembly line, and the increased demands for higher reliability.
Packaging materials have been developed for electrostatic discharge protection. U.S. Pat. No. 3,572,499, for example, discloses a composite laminated material in sheet form comprising a layer of thin sheet metal, typically aluminum foil, a layer of protective material secured to one face of the metal layer (to form the outside of a package or container) and an exposed layer of an electrically conductive, synthetic organic polymeric plastic material (to form the interior surface of the package or container). The protective material is preferably paper or fabric, and the conductive plastic material is preferably polyethylene filled with a non-metallic filler such as carbon.
U.S. Pat. Nos. 4,156,751 and 4,154,344 disclose a flexible sheet material for forming an envelope used to enclose and protect electronic components from electrostatic charges. The envelope includes a polymeric sheet, an antistatic material disposed at an inner surface, and a conductive layer disposed on the outer surface. The inner, antistatic layer acts as a humectant surface to collect water to reduce friction and minimize static charges. The external (metallized) layer has light transmissivity of at least 25 % (optical density of at the most 0.6).
U.S. Pat. No. 4,424,900 discloses an anti-static package composed of a multi-ply flexible film. The inner ply is an antistatic material and the outer ply is an electrically insulating material. A conductive metallic ply is sandwiched between the inner and outer ply. The antistatic ply is an antistatic polyolefin material; the metallic ply is a thin sputtered layer of, e.g., stainless steel, preferably having a light transmission in excess of 70% (optical density of at most 0.15).
U.S. Pat. No. 4,699,830 discloses a laminated sheet material which can be used to form packages for electrically sensitive components. The laminated sheet includes an antistatic layer, a first and a second conductive metal layer, and a carrier film layer. The antistatic layer can be a polyolefin-based material. The metal layers are vacuum deposited layers, preferably thin enough to permit light transmission in combination of 15-70% (o.d. 0.15-0.82).
U.S patent application Ser. No. 07/386,765, filed Aug. 2, 1989, describes an electroconductive powder composition comprising a amorphous silica particles which are uniquely associated with a two-dimensional network of antimony-containing tin oxide crystallites. This powder can be incorporated as a component within a polymeric carrier matrix which can take the form of a paint film, fiber, or a variety of shaped articles.
Many of the prior art packages or films employ antistatic agents which are moisture dependent or which consist of carbon particles, but which can also contaminate sensitive electronic components. Furthermore, such packages do not always provide the most satisfactory barrier properties against moisture or other contaminants. Many such packages, in addition, can be bulky, stiff, or too thick to be readily used in automated packaging machinery. The present invention provides new packaging materials for protective packaging of electrostatic, radio frequency interference, and moisture sensitive electronic components or assemblies, readily usable in automated form, fill, and seal packaging machines, thus overcoming many of the deficiencies of prior art materials.